It is known to provide a source of electromagnetic radiation and cause it to reflect perpendicularly from a surface of a sample so that the orientation of the source of the electromagnetic beam is known, then to rotate/tilt the sample to set it such that said electromagnetic beam approaches it along an oblique angle, and then to move the sample in a direction perpendicular to its surface so that a reflected electromagnetic beam enters a present data detector. Said technique is utilized in the J.A. Woollam CO. VUV-VASE System, for instance.
It is also known to focus a beam of electromagnetic radiation which approaches a surface of a sample onto a very small spot and reflects therefrom, and without tending to any sample rotation/tilting move the sample along a substantial perpendicular to said sample surface until a reflected beam optimally enters a present detector. Where a focused beam is utilized the spot size is sufficiently small that a slight tilt of the sample has little effect on the trajectory of the reflected beam. This technique is utilized in systems produced by Nanometrics Inc.
The above recited approaches to aligning a sample with respect to an electromagnetic beam, it should be appreciated, utilize only one beam of electromagnetic radiation.
A Co-Pending Application discloses a system for controlling the angle of incidence and angle of azimuth at which a beam of electromagnetic radiation obliquely impinges on a monitored location of a surface of a sample which comprises a sample supporting stage which can be translated in “X”, “Y” and “Z” directions as well as rotated about “X”, “Y” and optionally “Z” axes. (Note that this is to be interpreted to include rotating and translating the ellipsometer such that relative positioning of the sample and ellipsometer is achieved). Said system is primarily for application with samples with irregular surfaces, or small samples. Vertically, as viewed in side elevation, above said stage there is a first beam splitter means, a lens and a first camera means for providing a view of a portion of the surface of said sample, said first beam splitter means having optionally positioned below a lower surface thereof, light emitting means for providing light to the surface of said sample. Laterally with respect to said first beam splitter means there being a reflection means, and vertically above said reflection means there being a second beam splitter. Vertically above said second beam splitter there is a second camera means and laterally with respect to said second beam splitter, there is sequentially a lens and an essentially point source of electromagnetic radiation. Said first and second camera means each have associated therewith display means. Said system further comprises an ellipsometer polarization state generator to cause, and a polarization stage detector to monitor, a beam of electromagnetic radiation which in use impinges on said monitored location on said surface of said sample at an oblique angle thereto. In use said first camera means and its associated display means provide a view of at least a portion of the surface of a sample utilizing light provided by said light emitting means for providing light to the surface of said sample positioned on said lower surface of said first beam splitter, and said essentially point source of a source of electromagnetic radiation provides electromagnetic radiation to the surface of said sample via said second beam splitter, said reflective means and said first beam splitter. Said sample supporting stage is caused to be translated in any of said “X”, “Y” and “Z” directions as well as rotated about said “X”, “Y” and optionally “Z” axes which are necessary to cause an interrogating beam of electromagnetic radiation provided by said essentially point source, (eg. a fiber optic), of a source of electromagnetic radiation to reflect from the surface of said sample, proceed back through said first beam splitter means, reflect from said reflective means, pass through said second beam splitter means, enter said second camera means and cause an image on the display means associated therewith which indicates, (eg. via an electronically generated cross-hair), that the monitored location on the sample surface is oriented so as to face substantially vertically. The purpose is to align said sample surface to assure that said beam of electromagnetic radiation provided to said monitored location on the surface of said sample at an oblique angle approaches said surface at a known intended angle of incidence thereto, rather than at an angle of incidence which is modified by surface irregularities or non-flat samples, (eg. wedge shaped). A problem can develop in that an interrogation beam spot can appear in the image of the first camera means display as part of the interrogation beam and proceed through said first beam splitter thereinto. As a solution to this problem, said system can further provide that a polarizer means be placed into the path of said beam of electromagnetic radiation provided by said essentially point source of a source of electromagnetic radiation, and in which said first beam splitter is sensitive to polarization state. The polarizer means is preferably adjustable to enable changing the direction of imposed polarization. This can be beneficial where, for instance, the sample has an effect on the reflected interrogation beam polarization state, and where it is determined desirable to allow some of said interrogation beam to reach the first camera means, (eg. where it is found to aid with sample surface alignment).
It is noted as an introduction to the following method that when the sample surface is oriented to face substantially vertically at said monitored location, limited range “X” and/or “Y” translation has essentially no effect on said image on the display means associated with said second camera means, thereby indicating that the monitored location on said sample surface is oriented so as to face substantially vertically over said limited range of “X” and “Y” translation. (It is noted that a standard ellipsometer alignment detector means is used to achieve this step). Of course gross “X” and/or “Y” translation does have an effect which is representative of surface irregularities.
It is noted that a sample with surface irregularities was used as an example in the foregoing, but the sample can also be very small, (eg. millimeter dimensions), which presents similar alignment difficulties.
The method of calibration involving orientating a monitored location on a sample, said sample being characterized by:                it has surface irregularities, or        it is small in dimension;comprises the steps of:        
a) providing a stage for supporting a sample, said stage having means for effecting translation in any of said “X”, “Y” and “Z” directions as well as rotation about said “X”, “Y” and optionally “Z” axes;
b) placing a sample characterized by a selection from the group consisting of:                it has surface irregularities,        it is small in dimension;onto surface onto said stage;        
c) causing an interrogating beam of electromagnetic radiation to impinge on said monitored location on said sample;
d) monitoring the effect of “X” and “Y” direction translation on the locus of reflected beam electromagnetic radiation from the surface said sample and if either said translation causes significant change therein practicing step e, and if neither said translation causes significant change therein terminating the practice of said method;
e) adjusting rotation of said stage about at least one of the “X” and “Y” directions and again monitoring practicing step d.
Said method of calibration can further comprises at least one “Z” direction translation to better enable monitoring the effect of “X” and “Y” direction translation on the locus of reflected beam electromagnetic radiation from the surface of said sample.
While a specific Search was not conducted, known patents are disclosed to aid the Examination:                patent to Coates U.S. Pat. No. 4,373,817;        patent to Coates U.S. Pat. No. 5,045,704;        RE. 34,783 to Coates;        patent to Mikkelsen et al., U.S. Pat. No. 6,600,560;        patent to Fanton et al., U.S. Pat. No. 5,596,411;        patent to Piwonka-Corle et al., U.S. Pat. No. 5,910,842;        patent to Piwonka-Corle et al., U.S. Pat. No. 5,608,526;        patent to Bareket, U.S. Pat. No. 5,889,593;        patent to Norton et al., U.S. Pat. No. 5,486,701;        patent to Aspnes et al., U.S. Pat. No. 5,900,939;        PCT Application Publication WO 99/45340;        Published Application of Stehle et al., No. US2002/0024668 A1;        
While the known prior art and a previously disclosed system and method provide means for aligning a sample, there remains need for a simple system and method for aligning samples in ellipsometer, polarimeter, reflectometer, spectrophotometer and the like systems, particularly where applied to large area samples.